Innovation in the carbonated beverage bottling industry is very much dependent on the ready availability of machinery for processing new types of containers and/or closures. For years, the crown was the dominant closure employed and only in the last fifteen years was there any significant swing to a different type of closure, which comprised a cap shell of aluminum which was inserted over the threaded neck end of the container and then secured in place by rolling threads in situ into the walls of the cap shell. Such closures are commonly called roll-on caps. This type of closure application necessarily required a completely new applicating machine because not only was an axial force necessary to hold the closure in place on the bottle neck and to form a seal between the closure liner and the end of the bottle neck, but concurrently, a rotating movement had to be imparted to the thread forming rollers. There was no way that a conventional crown-type applicating machine could be modified to apply the new style roll-on closures and, as a result, the adoption of the new closure proceeded very slowly.
However, it did proceed and practically every carbonated beverage bottler now has a machine installed in his bottling line that is capable of applying an aluminum shell on the neck of a bottle and rolling threads into the shell to effect the threaded securement of the roll-on closure to the bottle.
In recent years, there have been significant developments in plastic technology making the utilization of a threaded plastic closure completely feasible for use in the carbonated beverage field. For example, a threaded closure of the type shown in U.S. Pat. Nos. 3,987,921 and 4,016,996 has been shown to be commercially practicable, and would be an economically desirable change for the average bottler to adopt, if he did not have to invest in new applicating machinery to assemble this style closure to the bottle neck.
Since this particular closure requires a concurrent application of an axial force to the top panel of the closure with a rotation of the closure relative to the bottle neck, it would obviously be desirable to attempt to utilize the existing closure applicating machines for effecting the assemblage of aluminum shells to bottle necks to apply this new style plastic closure, and thus greatly minimize the capital investment required for the average bottler to adopt the new plastic closure.
There is, therefore, a distinct need for an inexpensive capping head which may be applied to existing roll-on closure applicating machines for effecting the assemblage of plastic screw thread type closures to bottle necks.
Any such new capping head must also incorporate mechanism for limiting the maximum torque applied to the closure. Since the closure is fabricated from a thermoplastic material, it is subject to tearing and/or cracking if an excessive applicating force is applied. Moreover, it is necessary that the maximum applicating torque be maintained substantially constant, irrespective of the ambient conditions, and particularly independent of the ambient humidity conditions, which vary widely in a bottling plant, particularly in the morning start up period of the plant.